1. Field of the Invention
The present invention relates to flocculant injection and mixing apparatus for use in dewatering sewage, industrial waste, sludge, and other contaminated aqueous material. When mixed with the aqueous material, the flocculant aids the separation of the contaminating solids from the aqueous medium.
2. Background of the Invention
Prior to dewatering sludge, sewage, or industrial waste, it must be mixed with a flocculant that causes the solid waste matter to aggregate into floccules. These floccules settle to the bottom of the container allowing the water to be easily removed by filtering or decanting.
Long chain polymers are frequently used as flocculators for conditioning and dewatering sludge. To achieve the highest degree of flocculation, however, the polymer must be dispersed within the aqueous material as evenly and rapidly as possible. A uniform distribution of polymer insures that the maximum amount of solid material is flocculated with the minimum amount of polymer. Furthermore, the polymer must be rapidly mixed with the aqueous material because most polymeric flocculators have an extremely short reaction time.
Three basic types of flocculant injection and mixing systems are presently used in the treatment of sludge and sewage. The first type employs a web-like sparger ring located within the conduit carrying the aqueous material. The sparger ring's webbing has channels that face upstream and the flocculant is injected into the sewage through these channels. Mixing of the flocculant and aqueous material takes place due to the currents and eddies caused by the aqueous material flowing passed the webbing of the sparger ring.
This first type of injection and mixing system, however, is ineffective when the flow carrying conduit is of a relatively small diameter, because the currents and eddies caused in such pipes are insufficient to uniformly mix the flocculant and the aqueous material. Furthermore, if the aqueous material has a high solids content (i.e., greater than 2%), the webbing of the sparger ring tends to trap the solid matter and clog the conduit. The dewatering system must then be shut down, at great cost, until the conduit can be cleared.
The second type of known polymer injection system introduces the flocculator through a series of holes on the periphery of the flow carrying conduit. The flocculant and the aqueous material are mixed as the aqueous material passes a series of static devices that are located downstream from the injection holes. Examples of such static devices are baffles mounted on the inside of the pipe and pipe fittings designed to abruptly change the direction of flow.
This second type of mixing system is generally less effective in dispersing the flocculant than the first type. Complete dispersion of the flocculant depends upon the fluid traversing the series of static devices. Since the traverse time is usually greater than the brief reaction time of polymeric flocculants, the polymer is largely inactive by the time it is mixed with the waste material. Also, aqueous materials having a high solids content do not create liquid shear forces around the static devices that are sufficient to evenly disperse the flocculant. Additionally, the baffles used in some of these injection and mixing systems can cause clogging of the flow carrying conduit.
The third type of known system injects flocculant into the flow carrying conduit as a constant stream. The necessary mixing is then performed by mechanical devices, such as propellers or turbine mixers, mounted either within the conduit or within a separate tank.
This third system is the least effective of the three because the dispersion of the flocculant depends entirely upon the liquid shear forces generated by the propeller or turbine means. Thus, regardless of the shape of the fluid container, polymeric flocculant cannot be equally dispersed throughout the entire container within the brief reaction time of the polymer. Furthermore, this third type of system requires a high energy input in order to produce enough liquid shear forces to cause any mixing.
Therefore, there is a need for a flocculant injection and mixing apparatus that is capable of evenly and rapidly dispersing flocculant within aqueous material of high or low solids content prior to dewatering. Furthermore, there is a need for an injection and mixing apparatus that is small and compact in size, economical to manufacture, easy to maintain and operate, and energy efficient. In addition, there is a need for a flocculant injection apparatus that will not clog the flow carrying conduit in the presence of aqueous material having a high solids content.